Chapter 36 - VILI Flashcards
Define ventilator-induced lung injury
injury to the lung caused by mechanical ventilation in experimental models
Define ventilator-associated lung injury
worsening of pulmonary function, or presence of lesions similar ARDS, in clinical patients that is thought to be associated with mechanical ventilation, +/- underlying lung disease
Volutrauma is a significant cause of VILI. What is the mechanism?
a. regional overdistension –> cyclic recruitment-derecruitment injury
b. extra-alveolar air results from increased alveolar pressures
c. injured alveoli are progressively unstable, collapsing at the end of expiration
d. increased end-inspiratory volume –> stretch injury
d. increased high end-inspiratory volume results in stretch injury
a. & c. describe shear injury (atelectrauma)
b. is the definition of barotrauma, likely occurs due to a combination of stretch injury and compromised lung
Beyond which time period does increased FiO2 (>50%) promote the production of reactive oxygen & nitrogen species?
24h
What occurs with short term FiO2 of 100%?
Absorption atelectasis, decreased oxygen diffusion capacity
List 3 pathologic changes (similiar to ARDS and VILI) that are seen in oxygen toxicity?
interstitial oedema hyaline membrane formation damage to the alveolar membrane altered mucociliary function fibroproliferation
Why does an open chest cause more pronounced shear injury?
Lungs are able to completely collapse at the end of expiration, not tethered to the chest wall
Which group had decreased mortality in the ARDSnet study?
6ml/kg had lower overall mortality than 12ml/kg (although lower tidal volume group incidentally received slightly higher PEEP and FiO2)
Describe recommended tidal volume, PEEP and PIP settings for preventative strategies for VALI
tidal volume 6-10ml/kg
PEEP minimum 5cm H20
limit PIP to 30cm H20
List 7 additional preventative strategies
subjective analysis of PV loop to guide PEEP & PIP
avoid patient-ventilator asynchrony
consider recruitment manoeuvres
maintain dogs in sternal most of the time
limit interstitial oedema
allow permissive hypercapnia
allow permissive hypoxemia
What type of damage may occur if tidal volumes are too low? How can this risk me ameliorated?
Risk of atelectasis - further shear injury
maintain at 6-10ml/kg, PEEP crucial to keep alveoli open
What is the minimum amount of PEEP needed to reduce VILI?
not established
5-10 cm H20 considered adequate in humans
What type of damage can occur if PEEP is too high? How can you avoid this?
Increased risk of stretch injury - total end-inspiratory volume is increased. monitor PIP or plateau pressure closely (limit to less than 30 cm H20)
Describe how can pressure-volume loops can be used to guide PEEP and PIP settings.
accurate static PV curve - deeply anaes/paralyzed stable patient, no asynchrony, measurement of plateau pressure using oesophageal pressure then define LIP & UIP using mathematical model
or can subjectively use dynamic PV loop to estimate
Upper inflection point = upper beak with big change in pressure and little change in volume (greatly decreased compliance) - overdistension? rationale behind using it to limit PIP
Lower inflection point = lower lip - compliance improves - bigchange in volume with modest change in pressure - overcoming the ‘opening’ pressure of small airways, point of lung recruitment? raising PEEP above this level may decrease atelectrauma/shear injury
What are the disadvantages of using pressure-volume loops for this purpose?
chest wall compliance, asynchrony & ventilator mode interferes
no proof of accuracy/benefit
no consensus over what LIP and UIP represent
